Obviously there are a lot of variables here and a good portion of them were touched on by others in the thread.

Home Depot typically uses Silestone which is a quartz material in line with Zodiaq or HanStone. Slabs of those typically are 63" x 120" (jumbo) or 55" x 120". The price will increase if the yield is pretty low and they have a lot of waste due to odd shapes (I doubt there would be any in your parents' kitchen but it's worth thinking about)

I'm in Georgia and when I'm pricing out bids for a commercial job our fabricator typically tells us to use $50-$57/sqft for Silestone (this includes install & templating). Keep in mind this is for a large quantity commercial job but Silestone isn't some premiere quartz. Since HD uses subcontractors they're going to put their own markup on whatever the fabricator is willing to do the work for so you're looking at probably ~$70-80/sqft for Silestone.

Depending on the edge detail that can be an additional ~$10-$12 a lineal foot (mitered / ogee / bullnose/ demi-bullnose are all added costs in lieu of your standard eased edge)

Assuming $80/sqft your parents would have to have around 113 sqft of countertops to get close to $9,000. That would need to be around 43lnft of countertops (including a 4" backsplash and no fancy edge detail).

Again, YMMV depending on your location and the demand in your area. To me it sounds like quite a lot unless your parents have a monstrous kitchen or a weird-shaped kitchen that would result in a super low-yield of material.

Ikea

I've yet to find ANY cabinet maker with reasonable prices (RTA or otherwise) that have better drawers than IKEA. Their drawers and adjustability are amazing.

Other manufacturer relies on 2 screws going through the drawer box and into the face plate, with a few mm adjustment each way and a pain in the ass to assemble in the first place

Additionally, IKEA has super high tolerances on their parts, they WILL fit perfectly if instructions are followed. Their lamination (look at corners and edges) is superior to most RTA cabinets that I've found where the fronts aren't real wood.

I've built 3 IKEA kitchens, I would love to find an RTA supplier with similar quality where I can truly custom order the width of the cabinets, but until I do that I will ALWAYS pick IKEA. Possibly with third party fronts, if IKEAs choices aren't to my liking.